This invention relates to a railroad freight car truck suspension which is used to carry a freight car over the rails of a railroad, and more particularly to a means for mitigating the detrimental effects of using a conventionally designed railroad freight car truck at both relatively high and low speeds, the high speed being in excess of 80 kmh (kilometers per hour) or 50 mph (miles per hour) and the low speed being less than 40 kmh or 25 mph in curves where excessive yaw is a critical problem.
A typical railroad freight car is provided with a pair of trucks located at opposite ends of the freight car to support its body. Such a truck is provided with a pair of wheelsets each of which comprises an axle, a pair of spaced wheels and a tapered roller bearing assembly mounted at each axle end, and the truck is pivoted to the body of the freight car to permit its trucks to negotiate a curve. A conventional truck, referred to as a xe2x80x9cthree piece truckxe2x80x9d includes a pair of longitudinal side frames with a pair of wheelsets extending between the side frames, at opposite ends of the side frames. By xe2x80x9clongitudinalxe2x80x9d is meant the direction in which a truck is translated along rails, or the direction in which the rails extend. The wheelsets are journalled to rotate about a horizontal axis to allow the truck to roll along rails. The side frames are interconnected by a bolster that is mounted to each side frame by inserting the bolster through a through-window known as a xe2x80x9cwindow openingxe2x80x9d in each side frame. The central lateral axis of the bolster in a freight car truck at rest, is essentially at right angles to the longitudinal central axis of a side frame. The bolster""s ends are supported on a set of springs in each side frame, to accommodate vertical, and to a smaller extent, lateral loads, and the springs are seated within spring seats on the side frame. The bolster is pivotally connected to the body of the freight car to provide the necessary connection between the body and the truck. The bolster may be displaced vertically relative to the frames, depending upon the loading of the bolster, but lateral displacement of the bolster is limited by vertical ears known as xe2x80x9cbolster gibsxe2x80x9d projecting from the bolster. The interface between the bolster and side frame includes spring loaded wedges (xe2x80x9cfriction wedgesxe2x80x9d) which fix the longitudinal movement of the bolster, and, to a lesser extent, control the vertical and lateral and rotational motions between the bolster and the side frames.
Because the friction wedges permit the transmission of longitudinal forces and rotational forces and/or torsional moments from the side frames to the bolster, any difference in the magnitude of these forces at each end of the bolster will, when the resistance due to friction between the bolster and car body is exceeded, cause pivoting of the bolster in the horizontal plane. In addition to such movement of the bolster any imbalance in the magnitude of vertical forces exerted on the spring-supported ends of the bolster caused by a first pair of wheels on one side of a pair of wheelsets, on one side of the truck, will tend to unload the other end of the bolster which will move vertically relative to the second pair of wheels of the wheelset on the opposite side of the truck. This accommodation of vertical movement allows the truck to travel over track which is uneven and maintains a good load distribution between the four wheels of the truck.
Though the conventional truck side frames provides a very stiff longitudinal constraint which maintains the wheelsets parallel to one another the conventional design is ineffective in keeping the wheelsets aligned in a lateral direction in the horizontal plane. The imposed lateral loads generated between wheel and rail at a high speed above 80 kmh on straight track and lower speeds below 40 kmh on curved track tend to rotate the side frames about the ends of the bolster allowing misalignment of the wheelsets or truck warping.
First, the action at higher speeds: the problem is exacerbated when there is warping or an in phase yaw displacement in which the wheel sets remain parallel to one another but not perpendicular to the side frames. This in phase yaw displacement is commonly known as lozenging and results in two undesirable characteristics. Firstly, an unstable condition known as hunting can occur in which the yaw displacements occur in a continuous oscillatory manner excited by the action of the wheels against the rails. Such a motion promotes high wheel and rail wear, causes high shock levels to be transmitted to the rails and the vehicle body and can, in extreme cases, lead to derailment of the vehicle.
The second action occurs on curves. When the vehicle travels on curves of sufficiently small radius to cause the leading wheelset to come into flange contact with the outer rail the wheelset experiences a yaw torque which turns it toward the outer rail. This creates a very high angle of attack of the leading axle with the rail and it is well known that such high angles of attack result in high levels of wear and noise as well as creating high force levels and the possibility of derailment.
One solution to such lozenging has been to use trucks having a rigid H frame. In this type of construction the bolster and side frames are integrally formed so that relative longitudinal displacement (in the direction of the rails) between the side frames cannot occur. Such frames tend to be extremely rigid so that their ability to accommodate vertical movement between the axles is not very good, and it has been shown that such rigidity results in a relatively low critical velocity, that is, the velocity at which instability occurs is typically less than 80 kmh.
It has also been suggested to use two braces extending diagonally between the side frames and bolted and/or welded to each other at their intersection. This construction is effective in controlling instability and improving xe2x80x9ccurvingxe2x80x9d since the construction has a high warp stiffness and is not rigid; however, it is subject to failure due to fatigue resulting from vibration.
In North America and in other countries that follow the North American practices, the conventional three-piece freight car trucks in railroad freight service have evolved to satisfy a variety of important operating and economic requirements. Freight car trucks must be capable of safely supporting and equalizing very high wheel loads over a wide range of track and operational conditions while delivering a high level of economic value. The three-piece trucks in service today are being challenged by ever increasing demands for improved performance. Effective Jan. 1, 2003, this demand for better performance reached a new level when the Association of American Railroads (xe2x80x9cAARxe2x80x9d) issued a new specification M-976-2002, xe2x80x9cTruck Performance Specification For Rail Cars,xe2x80x9d that sets the performance requirements for all freight car trucks. Most all current freight car truck designs are failing to meet all of the performance requirements of the new AAR specification. The main reason for the failure is the conflicting requirement for good vertical flexibility and high inter-axle shear stiffness or truck warp stiffness.
Freight car truck design requirement for the proper selection of suspension springs and friction dampers along with the proper selection of a higher than normally available interaxle shear stiffness was known in the early 1970""s (see AAR Track Train Dynamics Program Phase I and II). In order to meet the vertical suspension requirements larger friction damping wedges with higher damping forces were developed (see U.S. Pat. No. 5,511,489 to Bullock, inter alia). In order to increase the inter-axle shear stiffness various additional structures have been added to the three-piece freight car truck. These attempts include a spring plank connecting the spring seats of the truck side frames (Weber Patents and List U.S. Pat. No. 4,483,253), directly inter-connecting the wheelsets to each other through a sub-frame (U.S. Pat. No. 4,131,069 to List and U.S. Pat. Nos. 4,067,262; 4,067,261; and 4,151,801 to Scheffel) and inter-connecting the side frames to each other using a cross brace system (U.S. Pat. No. 4,570,544 to Smith). All of these designs increase the inter-axle shear stiffness to the proper level (greater than 40,000 pounds per inch) without affecting the vertical suspension system. However, none of these designs were generally accepted by the railroad industry due to economic factors and the additional weight the stiffening frames added to the freight car truck.
Another means for increasing the yaw stiffness between the truck side frame and bolster is to connect the bolster and side frame together with a stabilizing bar or anchor (U.S. Pat. No. 5,992,330 to Gilbert). This method has been used on railroad locomotives and passenger cars for over seventy years. These railroad vehicles have a very low net to tare ratio or very little vertical spring deflection from empty to loaded conditions. However, a railroad freight car, on the other hand, has a large change in weight from empty to loaded car conditions resulting in a much higher change in spring heights. Therefore, a fixed length bar or anchor cannot accommodate the different lengths required of it for the empty to loaded freight car spring deflections.
Since the 1970""s the generally accepted practice for increasing the inter-axle shear stiffness was to increase the yaw resistance between the side frame and truck bolster through changes in design of the friction wedge interface with the truck bolster pocket and side frame columns. This included wider friction wedges as in the ""489 patent, more acute wedge angles (U.S. Pat. No. 5,544,591 to Taillon) and split wedges, inter alia. These approaches to friction wedge design predominates the current freight trucks in North American railroad service. In order to meet the new AAR Specification M-976-2002 there are indications from recent tests that the wedging action within the vertical suspension that is required to give adequate interaxle shear resistance interferes (locks up) with the compliancy of the vertical suspension system to accommodate the required specified track conditions.
The yaw stabilization means disclosed herein provides a light-weight means for increasing the linear yaw stiffness levels between the side frame and bolster to provide the proper inter-axle shear stiffness without affecting the compliancy required of the vertical suspension system. This invention, which fails to increase the unsprung weight of a railroad car truck assembly noticeably, may be retrofitted to existing freight car trucks in service or incorporated into newly manufactured trucks.
The goal of this invention is to dispense with the need of using damping wedges to increase interaxle shear stiffness and allow the wedges to function optimally for control of vertical vibrations.
The stabilizing means comprises a xe2x80x9cyaw yokexe2x80x9d comprising a xe2x80x9cpivot barxe2x80x9d and a pair of oppositely disposed diverging spring arms. The pivot bar is pivotable on a pivot means, preferably a ball-pivot, fixed at the longitudinal central axis of the side frame. The pair of diverging spring arms extend towards the bolster on either side of the longitudinal axis through the ball-pivot; one spring arm lies in a position inside the longitudinal axis and is referred to as the xe2x80x9cinside spring armxe2x80x9d; lying inside the truck, the inside spring arm is not visible from outside the truck. The other spring arm lies in a position outside the longitudinal axis and is referred to as the xe2x80x9coutside spring arm.xe2x80x9d To connect the inside spring arm to the bolster near the end thereof, but inside of the truck (inside the longitudinal axis of the side frame), the bolster is provided with an anchoring means in the form of an anchoring stub welded to the bolster, the stub having a xe2x80x9ccoupling endxe2x80x9d, for example, a hooked end or more preferably a ring, to couple with one end of a linking means, preferably a xe2x80x9ccoupling linkxe2x80x9d (this one referred as a xe2x80x9cfirst linkxe2x80x9d) such as one conventionally used in chain assemblies to hoist heavy objects. The term xe2x80x9clinking meansxe2x80x9d is used to describe the interconnection of structural elements of the yaw stabilizer, irrespective of how they are connected to serve the purpose of a link. The other end of the first link is linked or coupled to the end of the inside spring arm, which, like the anchoring stub, is provided with a coupling end, for example, a hooked end, or more preferably a ring. To connect the outside spring arm to the bolster, preferably at the end thereof, outside the longitudinal axis of the side frame, the bolster is provided with a rocker arm pivotable about a vertical rocker pin. One end of the rocker arm is provided with a coupling end to which a second coupling link (this one referred to as a xe2x80x9csecond linkxe2x80x9d) is coupled; the other end of the second link is coupled to the end of the outside spring arm. The other end of the rocker arm is provided with a through-passage having a Spiralock female thread with a bolt and jam nut, allowing the end of the rocker arm to be forced away from the bolster""s surface when the bolt (xe2x80x9cpre-loading boltxe2x80x9d) is tightened against the bolster""s surface and locked in place by the jam nut.
The loading bolt provides a critical function for optimum performancexe2x80x94it preloads the arms of the pivot bar to a pre-determined load required for the proper truck initial inter-axle shear resistance and shear rate. In addition, for proper inter-wheelset shear spring rate, the vertical plane through a linking means, and, a vertical plane through the first pivot means and an end of the linking means held in the end of the first arm of the pivot bar, forms an acute angle. To provide a desired loading, the coupling end of the stub anchor is positioned for optimum performance of the truck under designated conditions. The location of the coupling end which determines the position of one end of the link may be calculated by one skilled in the art.
In the foregoing configuration, adjustment of the stabilizing means for the truck may be readily made by torquing the pre-loading bolt from outside the truck. Because the position of the coupling end on the anchoring stub inside the truck is fixed, no adjustment of anything inside the truck is required.